Method and apparatus for controlling exhaust gas recirculation and start of combustion in reciprocating compression ignition engines with an ignition system with ionization measurement

ABSTRACT

An apparatus and method to detect combustion conditions using ion signals for use in a feedback control of a reciprocation engine is presented. The ion signals are used as a feedback signal to control EGR and diesel injection timing. The apparatus is an ignition system with a spark plug type of sensor. The ignition system is used to provide a cold start mechanism for diesel engines and start of combustion for spark ignition engines. The ignition is combined with ion sensing feedback that can control the engine.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This patent application is a Continuation of U.S. patent applicationSer. No. 10/576,989 filed Dec. 19, 2006, which is a national stage ofPCT/US2004/035651 filed Oct. 27, 2004, which claims the benefit of U.S.Provisional Patent Application No. 60/516,148, filed Oct. 31, 2003, theentire teachings and disclosure of which are incorporated herein byreference thereto.

FIELD OF THE INVENTION

The present invention relates generally to ignition systems withionization feedback in diesel engines, and more particularly relates tosuch systems in reciprocating compression ignition engines in which coldstart combustion is started with a plasma discharge ignition system.

BACKGROUND OF THE INVENTION

Government agencies and are reducing the amount of allowed emissions indiesel and other compression ignition engines in an effort to reducepollution in the environment. For example, over the past decade,increasingly more stringent heavy duty on-highway engine emissionregulations have led to the development of engines in which NO_(X) anddiesel particulate emissions have been reduced by as much as seventypercent and ninety percent, respectively. Proposed regulations for newheavy duty engines require additional NO_(X) and diesel particulateemission reductions of over seventy percent from existing emissionlimits. These emission reductions represent a continuing challenge toengine design due to the NO_(X)-diesel particulate emission and fueleconomy tradeoffs associated with most emission reduction strategies.Emission reductions are also desired for the on and off-highway in-usefleets.

Traditionally, there have been two primary forms of reciprocating pistonor rotary internal combustion engines. These forms are diesel and sparkignition engines. While these engine types have similar architecture andmechanical workings, each has distinct operating properties that arevastly different from each other. The diesel engine controls the startof combustion (SOC) by the timing of fuel injection. A spark ignitedengine controls the SOC by the spark timing. As a result, there areimportant differences in the advantages and disadvantages of diesel andspark-ignited engines. The major advantage that a spark-ignited naturalgas, or gasoline, engine (such as passenger car gasoline engines andlean burn natural gas engines) has over a diesel engine is the abilityto achieve extremely low NO_(X) and particulate emissions levels. Themajor advantage that diesel engines have over premixed charge sparkignited engines is higher thermal efficiency.

One reason for the higher efficiency of diesel engines is the ability touse higher compression ratios than spark ignited engines because thecompression ratio in spark ignited engines has to be kept relatively lowto avoid knock. Typical diesel engines, however, cannot achieve the verylow NO_(X) and particulate emissions levels that are possible withpremixed charge spark ignited engines. Due to the mixing controllednature of diesel combustion a large fraction of the fuel exists at avery fuel rich equivalence ratio, which is known to lead to particulateemissions. Spark ignited engines, on the other hand, have nearlyhomogeneous air fuel mixtures that tend to be either lean or close tostoichiometric, resulting in very low particulate emissions. A secondconsideration is that the controlled combustion in diesel engines occurswhen the fuel and air exist at a near stoichiometric equivalence ratiowhich leads to high temperatures. The high temperatures, in turn, causehigh NO_(X) emissions. Lean burn spark ignited engines, on the otherhand, burn their fuel at much leaner equivalence ratios which results insignificantly lower temperatures leading to much lower NO_(X) emissions.Stoichiometric spark ignited engines, on the other hand, have highNO_(X) emissions due to the high flame temperatures resulting fromstoichiometric combustion. However, the virtually oxygen free exhaustallows the NO_(X) emissions to be reduced to very low levels with athree-way catalyst.

Recently, some members of industry have directed their efforts toanother type of engine that utilizes homogeneous charge compressionignition (HCCI) to reduce emissions. Engines operating on HCCIprinciples rely on autoignition of a premixed fuel/air mixture toinitiate combustion. The fuel and air are mixed, in the intake port orthe cylinder, before ignition occurs. The extent of the mixture may bevaried depending on the combustion characteristics desired. Some enginesare designed and/or operated to ensure the fuel and air are mixed into ahomogeneous, or nearly homogeneous, state. Additionally, an engine maybe specifically designed and/or operated to create a somewhat lesshomogeneous charge having a small degree of stratification. In bothinstances, the mixture exists in a premixed state well before ignitionoccurs and is compressed until the mixture autoignites. HCCI combustionis characterized in that the vast majority of the fuel is sufficientlypremixed with the air to form a combustible mixture throughout thecharge by the time of ignition and throughout combustion and combustionis initiated by compression ignition. Unlike a diesel engine, the timingof the fuel delivery, for example the timing of injection, in a HCCIengine does not strongly affect the timing of ignition. The earlydelivery of fuel in a HCCI engine results in a premixed charge that isvery well mixed, and preferably nearly homogeneous, thus reducingemissions, unlike the stratified charge combustion of a diesel, whichgenerates higher emissions. Preferably, HCCI combustion is characterizedin that most of the mixture is significantly leaner than stoichiometricto reduce emissions, which is unlike the typical diesel engine cycle inwhich a large portion, or all, of the mixture exists in a rich stateduring combustion

Other members of industry have moved to “dual mode” engines that operateon both a gaseous fuel mixture and diesel fuel. These engines operate inHCCI mode at part load and in diesel mode or SI mode at full load. As aresult, dual fuel engines produce emissions similar to most conventionaldiesel and natural gas engines. In particular, in known dual modeengines using diesel fuel and natural gas at high load, only a smallamount of diesel fuel is required to start ignition and the emissionsproduced would be similar to a spark ignited natural gas engine. Underother conditions when substantial diesel fuel is injected, the emissionsproduced would be similar to a conventional diesel engine.

Regardless of engine type, it is required to detect engine combustionconditions during engine operation in order to monitor emissions. Of allthe measuring methods for detecting engine combustion conditions, ioncurrent measurement has been considered to be highly useful because itcan be used for directly observing the chemical reaction resulting fromthe engine combustion. However, ion current detectors are typicallyincorporated into glow plugs. For example, an electric conductive layermade of platinum is formed on a surface of the heating element of theglow plug and is electrically insulated from the combustion chamber andthe glow plug clamping fixture.

In these glow plugs, ignition and combustion of fuel are generallypromoted by a heating action of the glow plug heating element when theengine starts at low temperature. The heating state of the heatingelement usually continues after warm-up of the engine has been completeduntil the combustion is stabilized (generally, referred to as“afterglow”). After completion of the afterglow, the heating action ofthe glow plug is stopped and the process of detecting ion current isstarted. Carbon adheres to the circumference of the ceramic heatingportion of the glow plug and reduces the insulation resistance betweenthe exposed electrode used for ion current detection and the groundedportion (plug housing and cylinder head) that is insulated from theelectrode. In this case, a flow of leakage current may be createdthrough the adhered carbon even if no ion is derived from the combustiongases. When this happens, the ion current detected shows a waveformdifferent from a desired one due to occurrence of the leakage current,and such an incorrect detection result causes deterioration in theaccuracy of ignition stage and flame failure detections. Furthermore,the electrode is almost completely exposed into the combustion chamberand the space between the housing and the electrode is narrow. For thisreason, there is a danger that the electrode is shorted to the groundand the housing is made conductive due to adhesion of carbon to theelectrode surface, resulting in an error in detecting ion current.

Additionally, since the ion current detecting electrode supported at thetip of the glow plug directly touches a flame having a high temperature,stresses tend to be concentrated in the neighborhood of the ion currentdetecting electrode and could damage the ceramic glow plug such as tocrack it.

BRIEF SUMMARY OF THE INVENTION

In view of the foregoing, an object of the present invention is toreliably detect ionization signals in compression ignition engines anddual mode engines and use the ionization signals as feedback in thecontrol of the engines.

The foregoing object is among those attained by the invention, whichprovides a method and apparatus for reliably detecting ionizationcurrent and using the ionization current as feedback in the control ofthe invention. The ion sensor may be a spark plug type of sensor that isshielded completely or partially from direct impingement of fuel sprayand the engulfment of a diffusive flame or a sensing apparatusintegrated into the fuel injector of the combustion chamber. The sparkplug sensor may also be used to replace glow plugs to provide a coldstart mechanism for diesel ignition.

In addition to using the apparatus to provide cold starts for dieselignition, the apparatus is used in a control loop that controls theamount of exhaust gas recirculation (EGR) into an engine based on theion sensor's measurement of ionization current flowing in the combustionchamber.

Additional features and advantages of the invention will be madeapparent from the following detailed description of illustrativeembodiments, which proceeds with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings incorporated in and forming a part of thespecification illustrate several aspects of the present invention, andtogether with the description serve to explain the principles of theinvention. In the drawings:

FIG. 1 is a schematic view of a plasma ignition control of the presentinvention;

FIG. 2 is a block diagram view of the a portion of the plasma ignitioncontrol of FIG. 1;

FIG. 3 is a graphical illustration of pressure and ionization currentversus engine piston crank angle at various levels of NO_(X);

FIG. 4 is a graphical illustration of the first peak of ionizationcurrent versus engine-out emissions at various loads;

FIGS. 5-8 are graphical illustrations of pressure and ionization currentversus engine piston crank angle for various conditions of speed andload;

FIG. 9 is a graphical illustration of pressure and ionization currentversus engine piston crank angle from plug fouling;

FIG. 10 a is a schematic view of an embodiment of an ion sensor usedwith the present invention showing the ion sensor during a fuel sprayimpingement;

FIG. 10 b is a schematic of the ion sensor of FIG. 10 a during adiffusive flame engulfment;

FIG. 11 a is an isometric view of an end of a standard type of sparkplug;

FIG. 11 b is an isometric view of the spark plug of FIG. 11 a with ashroud attached;

FIG. 12 a is a schematic view of an alternate embodiment of an ionsensor used with the present invention in a sleeve integrated into afuel injector;

FIG. 12 b is an enlarged view of the ion sensor of FIG. 12 a;

FIG. 13 is a schematic view of a further embodiment of an ion sensorused with the present invention integrated into the nozzle tip of a fuelinjector;

FIG. 14 is a graphical illustration of pressure and ionization currentversus engine piston crank angle at various levels of EGR;

FIG. 15 is a flow chart illustrating the steps to control EGR based onionization current in accordance with the teachings of the presentinvention;

FIG. 16 a is a graphical representation of pressure and ionizationcurrent versus engine piston crank angle for a normal combustion event;

FIG. 16 b is a graphical representation of pressure and ionizationcurrent versus engine piston crank angle for a misfire event;

FIG. 16 c is a graphical illustration of experimental data showing acorrelation between indicated mean effective pressure of an enginecylinder and misfire that is used in sizing the floating bounded spaceof the present invention;

FIG. 17 is a flow chart illustrating the steps to prevent misfire usinga spark plug type of ion sensor;

FIG. 18 is a graphical illustration of average ion signals and averagepressure curves with injector timing changes of 2 degrees per step in adiesel engine having a load of 50 Nm and an EGR level of 50%;

FIG. 19 is a flow chart illustrating the steps to control injectiontiming using ionization current in accordance with the teachings of thepresent invention; and

FIG. 20 is a graphical illustration of average ion signals and averagepressure curves with various EGR levels in an engine having a load of 50Nm.

While the invention will be described in connection with certainpreferred embodiments, there is no intent to limit it to thoseembodiments. On the contrary, the intent is to cover all alternatives,modifications and equivalents as included within the spirit and scope ofthe invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides an apparatus and method to detectcombustion ion current in a diesel combustion engine and perform variouscontrol functions using ionization signals such as EGR (Exhaust GasRecirculation) control, diesel injection timing control from ignition,and cold starts of diesel engines. As used herein, the term “compressionignition engine” refers to typical reciprocating diesel engines, HCCIengines and dual mode engines.

Turning to the drawings, wherein like reference numerals refer to likeelements, the invention is illustrated as being implemented in asuitable operating environment. Referring initially to FIG. 1, a system100 exemplifying the operating environment of the present invention isshown. The system includes an ionization module 102, a plasma driver104, an engine electronic control unit (ECU) 106, and a compressionignition engine. The ionization module 102 communicates with the ECU 106and other modules via the CAN (Controller Area Network) bus 108. Thecompression ignition engine includes engine cylinder 110 (e.g., acombustion chamber) that has a piston 112, an intake valve 114 and oneor more exhaust valves 116. An intake manifold 118 is in communicationwith the cylinder 110 through the intake valve 114. An exhaust manifold120 receives exhaust gases from the cylinder 110 via exhaust valve(s)116. The intake valve and exhaust valve(s) may be electronically,mechanically, hydraulically, or pneumatically controlled or controlledvia a camshaft. A fuel injector 122 injects fuel 124 into the cylinder110 via nozzle 126. An ion sensing apparatus 128 is used to sense ioncurrent and in one embodiment, ignites the air/fuel mixture in thecombustion chamber 130 of the cylinder 110 during cold start of theengine. The plasma driver 104 provides power to the ion sensingapparatus 128 to provide a high energy plasma discharge to keep the ionsensing detection area of the ion sensing apparatus clean from fuelcontamination due to carbon buildup. While shown separate from the fuelinjector 122, the ion sensing apparatus 128 may be integrated with thefuel injector 122. The exhaust manifold 120 is in fluid communicationwith EGR valve 132. The EGR valve is controlled by EGR module 134. TheEGR valve 132 provides exhaust gas to the intake manifold 118. Forsimplicity, the recirculation path from the EGR valve 132 to the intakeis designated by arrows 136. In some systems, the exhaust gas may befurther cooled by means of a cooler in the exhaust gas recirculationpath. Additionally, the exhaust valve(s) 116 can be controlled withvariable timing to assist in keeping some of the exhaust gas in thecylinder 128. While the ionization module 102, the plasma driver 104,the engine control unit 106, and the EGR module 132 are shownseparately, it is recognized that these components may be combined intoa single module or be part of an engine controller having other inputsand outputs.

The ionization module contains circuitry for detecting and analyzing theionization signal. In the illustrated embodiment, as shown in FIG. 2,the ionization module 102 includes an ionization signal detection module140, an ionization signal analyzer 142, and an ionization signal controlmodule 144. In order to detect combustion conditions, the ionizationmodule 102 supplies power to the ion sensing apparatus 128 after the airand fuel mixture is ignited and measures ionization signals from ionsensing apparatus 128 via ionization signal detection module 140.Ionization signal analyzer 142 receives the ionization signal fromionization signal detection module 140 and determines if an abnormalcombustion condition exists. The ionization signal control module 144controls ionization signal analyzer 142 and ionization signal detectionmodule 140. The ionization signal control module 144 provides anindication to the engine ECU 106 as described below. In one embodiment,the ionization module 102 sends the indication to other modules in theengine system. While the ionization signal detection module 140, theionization signal analyzer 142, and the ionization signal control module144 are shown separately, it is recognized that they may be combinedinto a single module and/or be part of an engine controller having otherinputs and outputs.

Returning now to FIG. 1, the ECU 106 controls fuel injection 122 todeliver fuel (and air), at a desired rate and amount, to the enginecylinder 110. The ECU also controls the amount and rate of exhaust gasbeing recirculated into the combustion chamber 130. The ECU 106 receivesfeedback from the ionization module and adjusts the fuel and EGR asdescribed below.

The ionization signal can be correlated to the level of NO_(X) emissionand in-cylinder pressure produced during compression. Turning now toFIG. 3, the correlation between cylinder pressure traces, ion currenttraces and NO_(X) levels is shown. Curves 300 to 310 are ion currenttraces and curves 320 to 330 are cylinder pressure traces. Curves 300and 320 correspond to a λ of 1.58 and a NO_(X) level of 3.2 gr/BHP*hour,where

$\lambda = {\frac{{Actual}\mspace{14mu}{{air}/{fuel}}\mspace{14mu}{ratio}}{{Stochiometric}\mspace{14mu}{{air}/{fuel}}\mspace{14mu}{ratio}}.}$Curves 302 and 322 correspond to a λ of 1.60 and a NO_(X) level of 1.9gr/BHP*hour. Curves 304 and 324 correspond to a λ of 1.61 and a NO_(X)level of 1.2 gr/BHP*hour. Curves 306 and 326 correspond to a λ of 1.62and a NO_(X) level of 1.1 gr/BHP*hour. Curves 308 and 328 correspond toa λ of 1.63 and a NO_(X) level of 0.79 gr/BHP*hour. Curves 310 and 330correspond to a λ of 1.64 and a NO_(X) level of 0.35 gr/BHP*hour. It canbe seen that as the NO_(X) level decreases from 3.2 gr/BHP*hour to 0.35gr/BHP*hour, the magnitude of the ion signal and the location of itspeak vary in a consistent trend. Similarly, the cylinder pressure tracesfollow the same trend exhibited by the ion current traces. FIG. 4illustrates how the amplitude of the first peak of the ion currentchanges with respect to NO engine out emissions. Operating parameters ofthe engine are an engine speed of 1600 rpm, a variable torque (25, 50,75 Nm), a variable start of ignition, and a variable amount of EGR (40%to 50%). The circles (some of which are identified with referencecharacter 400) represent actual data points and the line 402 is a fittedline based on the actual data points. From this figure, it can be seenthat the amplitude of the first peak of the ion current increases as theNO engine out emissions increase.

Turning now to FIGS. 5-8, the relationship between diesel combustionpressure and ion current at various speeds and loads is shown. FIG. 5shows the relationship of pressure 500 and ion current 502 at an enginespeed of 1500 rpm and a load of 50 ft-lb. The start of combustion 504and combustion duration 506 are also shown. FIG. 6 shows therelationship of pressure 600 and ion current 602 at an engine speed of1500 rpm and a load of 150 ft-lb. The start of combustion 604 andcombustion duration 606 are also shown. FIG. 7 shows the relationship ofpressure 700 and ion current 702 at an engine speed of 2000 rpm and aload of 150 ft-lb. The start of combustion 704 and combustion duration706 are also shown. FIG. 8 shows the relationship of pressure 800 andion current 802 at an engine speed of 2500 rpm and a load of 150 ft-lb.The start of combustion 804 and combustion duration 806 are also shown.From these figures, it can be seen that the rise of the ion current islocated proximate to or at the start of combustion and the width of theionization signal (i.e., the “crank angle” between the rise of the ioncurrent and the fall of ion current) approximately lines up with thecombustion duration that is derived from the combustion pressure.

From FIGS. 3-8, it can be seen that ion current signals can be used tocontrol and optimize engine performance. The ion sensing apparatus canbe a separate unit or it can be integrated with the fuel injector. Thesensor apparatus should be shielded from direct impingement of fuelspray from the fuel injector. If the fuel spray impinges the sensingmechanism, the ion current does not track combustion pressure becausethe fuel shorts the sensor. This is illustrated in FIG. 9 where it canbe seen that the ion current 902 does not track the combustion pressure900.

It should be noted that the preferred method of sensing ion current isto use a negative charge (i.e., negative voltage polarity) on theelectrode of the ion sensing apparatus. The reason for this is thathumidity (i.e., water vapor and high temperature steam) in theatmosphere and due to the combustion process has an affinity forpositive charge. When a positive charge electrode is used, the watervapor and steam react with the positive charge and “pull” positivecharge from the electrode. The net effect of this is that the magnitudeof the ion signal increases, which may result in erroneous readings. Inmany instances, the ion signal due to humidity reaction is difficult toremove as it often has a frequency spectrum that is similar to noise.

FIGS. 10 a-12 b illustrate various types of ion sensing apparatuses 126that may be used by the invention. Other types of ion sensors may beused. Turning now to FIGS. 10 a-10 b, a spark plug type of sensor isshown. FIGS. 10 a and 10 b show a block diagram of a spark plug type ofsensor. The sensor electrodes 1002, 1004 of sensor 1000 is shielded byshield 1006. The presence of the shield 1006 drastically reduces foulingof the sensor electrodes 1002, 1004 and sensor conduction area 1008 fromthe liquid fuel spray 1020. During combustion, the diffusive flame 1022is filtered through the induction orifices 1008, which causes primarilypremixed flame 1024 to occur within the sensor's shielded space 1010.The presence of the shield 1006 allows detection of combustion ions fromthe pre-mixed flame instead of the diffusive flame, thereby allowingcorrelation with combustion quality (e.g., NO_(X) emission level). Thesize, number, and direction of induction orifices 1008 are determined inone embodiment using design of experiments (DOE) as is known in the art.It should be noted that the shield does not have to completely enclosethe sensor electrodes 1002, 1004. Turning to FIGS. 11 a and 11 b, ashroud 1102 located at the sensor area can be attached to the sensorbody 1100 of the plug shown in FIG. 10 a. The shroud 1102 is sized suchthat fuel spray does not directly impinge the sensor electrodes 1002,1004 and sensor conduction area 1008. During operation, the sensorelectrodes 1002, 1004 can be energized with a high-energy current thatcreates a high-energy plasma discharge that keeps the sensor electrodearea clean from fuel contamination and carbon build-up.

As previously indicated, the spark plug sensor may also be used toreplace glow plugs to provide a cold start mechanism for dieselignition. Energy is provided to the spark plug sensor of sufficientmagnitude to create sparks that are able to ignite the diesel fuelmixture in the combustion chamber. The use of a shield/shroud overcomesthe failure of prior art spark ignition systems by keeping the plugsclean from spark plug fouling by diesel fuel. The plugs stay clean bythe super heating effects of the plasma sparks caused by the high-energyplasma discharge. High-energy plasma discharges are generated atcurrents in the ampere range as compared to high energy sparks that aregenerated in the hundreds of milli-amperes range. As describedhereinbelow, the ion sensor (e.g., the spark plug sensor) can detect andprevent abnormal engine conditions such as misfire to essentiallyprovide a safety net for the combustion process at low load, high EGR,or HCCI modes of combustion. By preventing misfire and igniting the fuelmixture via the spark action and using surface gap spark plugs, thespark plug sensor can lower the cold start emissions of a diesel engine.The spark plug sensor can replace the glow plugs used in systems andreduce or eliminate the need for block heaters and intake air heatersthat have been used to assist in the cold start process of a dieselengine. Additionally, the spark plug can be used to provide a highcurrent spark to prevent late combustion or prevent a misfire when theengine ECU (or ionization module) senses that combustion has not begunon time.

Turning now to FIGS. 12 a and 12 b, a fuel injector 112 with anion-sensing sleeve 1200 around the nozzle 114 is shown. The controls1208, 1210 for the sensor 1200 are routed down the injector 112 and arerouted to the ionization module 102 and driver 104 via connection 1202that is away from fuel injector inlet line 122. The controls comprisethe ion bias voltage and heating current control 1210 that heat theelectrode 1206 and a thermocouple 1208 for sensor temperature feedbackcontrol. It is important to keep the electrode 1206 at a sufficientlyhigh temperature (e.g., 700 C) to prevent the formation of electricallyconductive contaminants that can shunt the ion-sensing electrode, suchas carbon, on the surface of the wafer. The ion bias voltage and heatingcurrent control 1210 provide sufficient current to maintain or otherwisekeep the electrode 1206 at the desired temperature. In one embodiment,this is accomplished by heating the sensor sleeve 1204 (e.g., a ceramicwafer). The sensor sleeve 1204 can be made, for example, out of SiliconNitrate wafer, with an imbedded electrode 1206 made, for example, out ofTitanium Oxide.

Other types of arrangements integrating the ion sensor with the fuelinjector 112 can be described. For example, in another embodiment of theion sensor, the ion sensor is integrated directly into the nozzle tip ofthe fuel injector. This is illustrated in FIG. 13. Turning to FIG. 13, aheater 1300 and an ion sensing element 1302 are integrated directly intothe nozzle tip 114. The integrated heater 1300 is controlled via line1304 by driver 104. The heater 1300 keeps the temperature at around 700C to protect the ion sensor from contamination. The ion sensing element1302 is controlled by ionization module 102 via line 1306. The principleobjective is to integrate the ion-sensor in the fuel injector 112 toeliminate the need of adding an extra opening in the engine cylinderhead for the ion-sensor apparatus. Regardless of how the ion sensor isintegrated, a temperature control should be used that keeps theinsulating element of the sensor at sufficiently high temperature toprevent the formation of conductive contaminants that can short theion-sensing electrode. The integrated heater eliminates signaldeterioration due to fuel fouling by keeping the ion sensing element1302 clean from fuel contamination.

Now that the operating environment and various embodiments of the ionsensing apparatus have been described, the control functions that can beused with the ion sensing apparatus will be described. The ionizationsignal is acquired with respect to an engine parameter over thecombustion cycle. For example, the engine parameter may be crank angle,time after ignition, time from top dead center, etc. Crank angle is usedherein in its most generic sense to include all of these. For example,crank angle is intended to be generic to measurement of the enginerotational parameter no matter whether it is measured directly in termsof crank angle degrees, or measured indirectly or inferred bymeasurement. It may be specified with respect to top dead center, withrespect to ignition point, etc.

One function that can be controlled with ion signals is EGR (Exhaust GasRecirculation) control. It is known that more EGR in the air/fuelmixture lowers NO_(X) emissions, too much EGR causes misfires, too lowEGR may cause knock, and the right amount of EGR allows HCCI combustion.The ionization signal is used to control the level of EGR during steadystate and transient operation. Turning now to FIG. 14, the averagepressure and average ion current for four levels of EGR are shown.Curves 1400 to 1406 are average pressures and curves 1410 to 1416 areaverage ion currents. The engine operating parameters for the curves arethat the engine load is 75 Nm and the start of combustion is atapproximately 4 degrees after TDC for all curves. Curves 1400 and 1410are for an EGR level of 40%. Curves 1402 and 1412 are for an EGR levelof 45%. Curves 1404 and 1414 are for an EGR level of 50%. Curves 1406and 1416 are for an EGR level of 55%. Note that curves 1406 and 1416represent an engine condition where the engine has transitioned intoHCCI combustion. It can be seen from FIG. 14 that as the average levelof the ion signal lowers, the level of EGR increases, which results incorrespondingly lower NO_(X) emissions. Additionally, the timing ordelay after injection of fuel where the start of the ion current occurscorresponds to an EGR level. Based upon these relationships, the levelof EGR can be controlled from the level of the ion signal. In otherwords, the ion current signal can be used in a closed loop control tocontrol the amount of EGR admitted into a combustion chamber based onthe measurement of the ion signal. For example, as illustrated in FIG.15, the ion current can be used in a feedback loop in a closed loopcontrol system. The control system determines what the average ioncurrent level is for the desired level of EGR and adjusts the level ofEGR until the measured average ion current level is within a toleranceband of the average ion current corresponding to the desired level ofEGR using control techniques as known in the art.

The level of EGR can be maximized by increasing the level of EGR untilmisfire is reached. The misfire can be detected in any number of ways.One way that misfire can be detected is using the ion signal. Forexample, in one embodiment, the method described in U.S. Pat. No.6,742,499, entitled “Method And Apparatus For Detecting AbnormalCombustion Conditions In Lean Burn Reciprocating Engines”, herebyincorporated by reference in its entirety, is used. As describedtherein, the variation of an ionization signal that changes with respectto an engine parameter over a combustion event of the engine ismeasured, a floating bounded space is associated with the ionizationsignal, and a determination is made if a portion of the ionizationsignal is within the floating bounded space. An indication is providedthat the misfire condition has been detected if the portion of theionization signal is within the floating bounded space. The floatingbounded space and a starting point for the floating bounded space aredetermined. This includes receiving a set of ionization signals thatchange with respect to an engine parameter over a combustion event. Theset of ionization signals has ionization signals corresponding to normalcombustion conditions and ionization signals corresponding to a misfirecondition for the engine. The starting point and size of the floatingbounded space are adjusted such that selected portions of the ionizationsignals corresponding to the misfire condition reliably fall within thefloating bounded space and the ionization signals corresponding tonormal combustion conditions reliably fall outside the floating boundedspace.

Turning now to FIGS. 16 a-16 c, the floating box 1600 for a misfireevent is shown. FIG. 16 a is an illustration of a representativecylinder pressure 1602 and ionization signal 1504 of a normal combustioncondition. FIG. 16 b is an illustration of a representative cylinderpressure 1606 and ionization signal 1608 for a misfire condition. Arepresentative set of data points of the engine parameter for 70 enginecycles is shown in FIG. 16 c. The engine parameter used is the IMEP of acylinder. If the IMEP of any data point is below a selected amount, thedata point is classified as a misfire condition. The selected amountshould be set to a point that detects all the misfires. In oneembodiment, the selected amount is a predetermined percentage ofnominal. Data points 1610 in FIG. 16 c correspond to a misfirecondition. It can be seen that the ionization signal 1604 of a normalcombustion condition has an initial short flattened portion from theinitial starting point followed by a peaked portion. In contrast, themisfire condition remains substantially constant for a given duration.One characteristic of a misfire condition in the ionization signal formany engines is that a portion of the ionization signal remainssubstantially constant from the initial starting point 1612 of theionization signal for an extended interval as can be seen in FIG. 16 band can be confined within a bounded space. Other characteristics may beused.

The tuning process is used to determine the starting point and size ofthe floating box using the characteristics of the ionization signals.The tuning process adjusts the size and position of the floating box toreliably capture the misfire condition and exclude the normal combustioncondition. The starting point and size of the floating box is adjusteduntil the floating box is of sufficient size and at a location of theionization signal with respect to crank angle such that a portion of theionization signal of a misfire condition reliably remains within thefloating box 1600 for the duration of the floating box 1600 as shown inFIG. 16 b and leaves the floating box 1600 for a normal combustioncondition as shown in FIG. 16 a. This is accomplished by overlaying thefloating box on the ionization signals corresponding to the normal andabnormal combustion cycles shown in FIG. 16 c and adjusting the boxparameters (e.g., starting point (with respect to crank angle (i.e.,time) and ionization signal magnitude), duration, and height) tooptimize the box. For example, the floating box is superimposed onionization signals corresponding to the upper and lower extremes of datapoints 1610 (i.e., the misfire conditions) in the engine beingcharacterized and the box parameters are adjusted such that the portionof the ionization signal reliably remains within the box for eachcondition. The floating box is then superimposed on the ionizationsignal for the normal ionization signals that are closest in form to theionization signals for misfire conditions. For example, the ionizationsignals corresponding to data points 1612, 1614, and 1616 are likely tobe closest in shape or form to ionization signals corresponding tomisfire conditions. The floating box is then adjusted until the portionof the ionization signal of the normal combustion condition is notcaptured by the floating box. This process is repeated for all of theionization signals in the data set for the various engine operatingconditions (e.g., speed, engine load, desired air/fuel ratio, etc.) toensure that the floating box reliably captures misfire conditions andexcludes other conditions. The box parameters are then used duringengine operation to detect misfire conditions.

During operation, the ionization signal analyzer 142 receives theionization signal. It floats the floating box over the ionization signalin accordance with the box parameters. In one embodiment, the lowestmagnitude of the ionization signal is determined beginning at thestarting point of the floating box and ending at the boundary of thefloating box (i.e., for the duration of the floating box). For example,if the duration of the floating box is thirty degrees of crank angle,the lowest magnitude of the ionization signal is determined over thethirty degrees of crank angle. The starting point of the floating box isthen positioned at the starting point crank angle (i.e., time afterignition) at the lowest magnitude of the ionization signal. Theionization signal analyzer 142 then determines if the ionization signalremains within the floating box over the duration of the floating box.The ionization signal analyzer 142 provides an indication to theionization signal control module 144 that a misfire has been detected ifthe ionization signal remains within the floating box over the durationof the floating box. FIG. 16 b illustrates the ionization signalremaining within the floating box over the duration of the floating box.

The ionization signal control module 144 provides an indication to theengine ECU 106 of the misfire condition and to other modules asrequested. The ECU 106 determines what action to take. In the case ofEGR control, the ECU 106 commands EGR module 134 to reduce the amount ofEGR admitted into the engine until misfire is either no longer happeningor to a level of misfire that is acceptable for operation.

In one embodiment, the EGR module 134 adjusts the amount and/or rate ofEGR admitted into the engine by increasing the level of EGR until thearea under a running average of individual cycles of the ion currentsignal is at or below a specified threshold value. In other words, theintegral of the ion current signal is below a threshold value. In oneembodiment, the threshold value is zero. The running average at thepoint where the area under the ion current signal is at or below thespecified value (e.g., zero) is defined to be the misfire limit. Thelevel of EGR and/or the rate of EGR admitted into the combustion chamber130 are lowered to a highest level such that the average ionizationcurve for an engine condition is at the minimum level above the misfirelimit where misfire does not occur. In one implementation of thisembodiment, a target ion current waveform is set to the average ioncurrent corresponding to the predetermined amount above the misfirelimit. The real time average ion current waveform is compared to thetarget ion current waveform. The level and/or rate of EGR are adjustedso that the real-time average ion current waveform is within a tolerancewindow of the target ion current waveform. If a level of EGR is desired,the target ion current is lowered to increase the level of EGR from thepresent level corresponding to the present target ion current. Thetarget ion current is raised to decrease the level of EGR. In analternate implementation, the level of EGR is increased until anindividual ionization signal waveform has an area at or below thethreshold value (e.g., zero). A target level is defined to be therunning average of the ionization signal at the point that is one cyclebefore the individual signal waveform with the area at or below thethreshold value. In other words, the target level is set to be justabove the misfire limit. The level of EGR is then lowered to a levelsuch that the running average of the ionization signal stays at thetarget level (i.e., just above the misfire limit). One method to performthis is to determine the desired starting point or rise of the averageionization current above a threshold level (e.g., above a zero level)that corresponds to the desired EGR target level and compare thestarting point of the average ionization current during operation to thedesired starting point and adjusting the EGR level until the startingpoint of the average ionization current is within a tolerance window ofthe desired starting point.

One approach to compare the real-time average ion current waveform tothe target ion current waveform is to compare the location of a peak ofthe average ion current waveform to a peak of the target ion currentwaveform. For example, in some engines, the ionization signal has asecond peak that corresponds to the peak combustion chamber temperature.The level of EGR and/or the rate of EGR injection are adjusted such thatthe location of the peak (e.g., the second peak) of the average ioncurrent waveform is within a tolerance window of the peak of the targetion current waveform.

In another embodiment, the real-time angular delta between the start ofcombustion and the average peak location of the average ion currentwaveform is compared to the target angular delta between the start ofcombustion and the peak location of the target ion current waveform. Thelevel of EGR and/or the rate of EGR injection are adjusted such that thereal-time angular delta between the start of combustion and the averagepeak location of the average ion current waveform is within a tolerancewindow of the target angular delta between the start of combustion andthe peak location of the target ion current waveform. The level of EGRis increased if the real-time angular delta is advanced of the targetangular delta and is decreased if the real-time angular delta isretarded of the target angular delta.

In another embodiment, the level of EGR is adjusted by variablyactuating one of the exhaust valves for varying lengths of time duringthe intake stroke of the particular combustion chamber in order toachieve the desired level of EGR. Other exhaust valves are actuated in aconventional manner.

In a further embodiment, misfire is prevented via use of a spark plugtype of ion sensor. Turning now to FIG. 17, the engine is characterizedand a specified crank angle is determined where combustion of the dieselfuel mixture should have started prior to the crank angle being reachedfor various operating conditions. During operation, energy of a levelsufficient to cause a high energy spark is provided to the spark plugtype of ion sensor if combustion of the diesel fuel mixture has not beensensed prior to the specified crank angle. For example, if the rise ofion current has not been detected after the specified crank angle thatcorresponds to the desired start of combustion has passed, energy isprovided to the spark plug type of ion sensor so that a spark isproduced that ignites the diesel fuel mixture.

The ion sensor apparatus can also be used to control the start ofinjection in a direct injection reciprocating compression ignitionengine such as the injection timing of a diesel engine. Turning to FIG.18, average ion signals 1800-1804 and average pressure curves 1810-1814with injector timing changes of 2 degrees per step are shown. The dieselengine load is 50 Nm and the EGR level is 50% for all curves. Curves1800 and 1810 correspond to a start of combustion at two degrees beforetop dead center (BTDC). Curves 1802 and 1812 correspond to a start ofcombustion at top dead center. Curves 1804 and 1814 correspond to astart of combustion at two degrees after top dead center (ATDC). Curves1806 and 1816 correspond to a start of combustion at four degrees ATDC.It can be seen that the peak of the ion current and the location of thepeak changes with the injector timing. As the injector timing increasesbeyond TDC (i.e., start of combustion is at a higher degree ATDC), thepeak of the ion current increases and the location of the peak movesaway from TDC to an increasing number of degrees ATDC. Similarly, as theinjector timing moves before TDC, the peak of the ion current decreasesand the location of the peak moves to an increasing number of degreesBTDC. The rise of the ion signal also moves in the same relationship asthe location of the peak of the ion signal. This relationship is used tocontrol injection timing (e.g., start of combustion). For example, thecrank shaft angle can be determined by detecting when the ion currentsignal rises. The crank shaft angle is the angle at the point that theion current signal changes and starts to rise. Turning now to FIG. 19,the engine is characterized to determine crank shaft angles where therise of ion current should occur for various operating conditions. Thestart of fuel injection is controlled in a closed loop fashion bysensing where the crank shaft angle of the rise of the ion signaloccurs. This angle is compared to a desired crank angle based on theengine characterization. If the rise of the ion signal occurs at adifferent angle, corrective action is taken so that the crank shaftangle of the rise of the ion signal moves to within a tolerance windowof the desired angle of injection. In one embodiment, an average of atleast two prior cycles is used to determine an average of the rise ofion current.

The ion sensor apparatus can also be used to control the maximum powerof the compression ignition engine. One methodology to control themaximum power is to control the burn rate of the engine. The burn rateis the speed at which the combustion propagates across a cylinder. As anengine burns leaner, the combustion takes longer to propagate away fromthe ignition point. The slowing down of the combustion causes a longerburn time between the ignition point and the location in crank angleswhere approximately half of the mixture is burned. The position whereapproximately half of the mixture is burned is called the “50% BurnPoint” and is often measured in crank angle degrees. In one embodiment,the engine is characterized and the relationship between the second peakof the ion current waveform and burn rate is determined. In thisembodiment, the real time average of the crank shaft angle of the secondpeak of the ion current waveform is compared to a target crank anglethat corresponds to the desired burn rate according to the enginecharacterization. The rate of fuel admitted into a cylinder is adjustedsuch that the real time average of the angle of the second peak of theion current waveform is within a tolerance window of the target angle.If the real time average of the crank shaft angle of the second peak ofthe ion current wave form is advanced of the target angle, the rate offuel admitted into the combustion chamber is decreased until the realtime average of the crank shaft angle of the second peak of the ioncurrent wave form is within a tolerance of the target angle. Similarly,if the real time average of the crank shaft angle of the second peak ofthe ion current wave form is retarded of the target angle, the rate offuel admitted into the combustion chamber is increased until the realtime average of the crank shaft angle of the second peak of the ioncurrent wave form is within a tolerance of the target angle.

In an alternate embodiment, the burn rate can also be controlled byadjusting the amount and/or rate of EGR admitted into the engine. FIG.20 shows ion current and cylinder pressure for an engine operating witha fixed load. Curves 2000 to 2006 are curves of cylinder pressure andcurves 2010 to 2016 are curves of ion current. Curves 2000 and 2010 arecurves corresponding to an EGR level of 45%. Curves 2002 and 2012 arecurves corresponding to an EGR level of 50%. Curves 2004 and 2014 arecurves corresponding to an EGR level of 55%. Curves 2006 and 2016 arecurves corresponding to an EGR level of 59%. From these curves it can beseen that very high levels of EGR slow the burn rate down and lower therate of rise of cylinder pressure. By knowing this relationship for anengine, the burn rate can be controlled by determining a desired EGRpercentage associated with the desired burn rate and adjusting the EGRadmitted into the engine based on the ion current waveform.

It can be seen from the foregoing that an apparatus and method to detection current and perform EGR control, injection timing, and dieselignition cold starts has been described. The apparatus eliminates theneed for a glow plug by using a spark plug type of sensor or an ionsensor integrated onto a fuel injector. The spark plug type of ionsensor can also be used to provide cold start of diesel ignition atreduced levels of NO_(X). Signal deterioration of the ion sensor due tofuel fouling is eliminated by means of either a high energy plasmadischarge (or a heater) that keeps the sensor area clean from fuelcontamination. The spark plug type of sensor also allows detection ofcombustion ions from pre-mixed flame instead of diffusive flame, therebyallowing correlation of the combustion ions with combustion quality(e.g., NO_(X) emission level).

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the invention (especially in the context of thefollowing claims) are to be construed to cover both the singular and theplural, unless otherwise indicated herein or clearly contradicted bycontext. The terms “comprising,” “having,” “including,” and “containing”are to be construed as open-ended terms (i.e., meaning “including, butnot limited to,”) unless otherwise noted. Recitation of ranges of valuesherein are merely intended to serve as a shorthand method of referringindividually to each separate value falling within the range, unlessotherwise indicated herein, and each separate value is incorporated intothe specification as if it were individually recited herein. All methodsdescribed herein can be performed in any suitable order unless otherwiseindicated herein or otherwise clearly contradicted by context. The useof any and all examples, or exemplary language (e.g., “such as”)provided herein, is intended merely to better illuminate the inventionand does not pose a limitation on the scope of the invention unlessotherwise claimed. No language in the specification should be construedas indicating any non-claimed element as essential to the practice ofthe invention.

Preferred embodiments of this invention are described herein, includingthe best mode known to the inventors for carrying out the invention.Variations of those preferred embodiments may become apparent to thoseof ordinary skill in the art upon reading the foregoing description. Theinventors expect skilled artisans to employ such variations asappropriate, and the inventors intend for the invention to be practicedotherwise than as specifically described herein. Accordingly, thisinvention includes all modifications and equivalents of the subjectmatter recited in the claims appended hereto as permitted by applicablelaw. Moreover, any combination of the above-described elements in allpossible variations thereof is encompassed by the invention unlessotherwise indicated herein or otherwise clearly contradicted by context.

1. A method for controlling the maximum power of a reciprocating enginehaving at least one combustion chamber comprising the steps of:determining a target ion current at a target angle corresponding to adesired burn rate; comparing an average ion current signal and crankshaft angle to the target ion current at the target angle; and adjustingthe amount of fuel admitted into the at least one combustion chamberuntil the average ion current signal and the crank shaft angle arewithin a tolerance window of the target ion current at the target angle.2. The method of claim 1 further comprising the step of adjusting atiming of the injection of fuel admitted into the at least onecombustion chamber.
 3. The method of claim 1 further comprising the stepof adjusting a rate of the injection of fuel admitted into the at leastone combustion chamber.
 4. The method of claim 1 further comprising thestep of measuring the ionization current with a negative polarity ofionization on the electrode of an ion sensor.
 5. A method forcontrolling the maximum power of a diesel engine having a combustionchamber comprising the steps of: determining a target ion currentwaveform and a target angle corresponding to a maximum burn rate;comparing a real time average ion current waveform and crank shaft angleto the target ion current waveform at a target angle; and increasing atleast one of a rate of fuel admitted into the combustion chamber and anamount of fuel admitted into the combustion chamber until the averageion current waveform and the crankshaft angle are within a tolerancewindow of the target ion current waveform at the target angle.
 6. Amethod of controlling the maximum power of a diesel engine by maximizingthe second peak of the ion current waveform at a target anglecorresponding to a desired burn rate, the method comprising the stepsof: comparing a real time average of an amplitude and crank shaft angleof the second peak of the ion current waveform to the target angle; andadjusting one of a rate of fuel admitted into the combustion chamber andan amount of fuel admitted into the combustion chamber such that thereal time average of the angle of the second peak of the ion currentwaveform is maximized within a tolerance window of the target angle. 7.The method of claim 6 wherein the step of adjusting comprises the stepsof: if the real time average of the crank shaft angle of the second peakof the ion current wave form is advanced of the target angle, decreasingthe one of the rate of fuel admitted into the combustion chamber and theamount of fuel admitted into the combustion chamber until the real timeaverage of the crank shaft angle of the second peak of the ion currentwave form is within a tolerance of the target angle; and if the realtime average of the crank shaft angle of the second peak of the ioncurrent wave form is retarded of the target angle, increasing the one ofthe rate of fuel admitted into the combustion chamber and the amount offuel admitted into the combustion chamber until the real time average ofthe crank shaft angle of the second peak of the ion current wave form iswithin a tolerance of the target angle.
 8. The method of claim 6 whereinthe start of injection in a diesel engine is also controlled using theion current waveform, the method further comprising the steps of:comparing a measured crank shaft angle of the rise of ion current to atarget crank shaft angle of the rise of ion current corresponding to adesired start of combustion; and adjusting the injection timing suchthat the crank shaft angle of the rise of ion current is within atolerance window of the target crank shaft angle.
 9. The method of claim8 wherein the step of adjusting the injection timing comprises the stepsof: retarding a start of injection angle to move an early angle of therise of ion current towards the target crank shaft angle for the nextcycle; and advancing the start of injection angle to move a late angleof the rise of ion current towards the target crank shaft angle for thenext cycle.
 10. A method for controlling the maximum power of a directlyinjected reciprocating engine comprising the steps of: determiningtarget average ion current features at a target angle corresponding tothe fastest allowable burn rate; comparing a real time average ioncurrent signal features and crank shaft angle to the target average ioncurrent features and the target angle; and adjusting one of the rate offuel admitted into the combustion chamber and the amount of fueladmitted into the combustion chamber such that the real time average ioncurrent signal features and the crank shaft angle are within a tolerancewindow of the target average ion current features and the target angle.11. The method of claim 10 wherein the step of adjusting the one of therate of fuel admitted into the combustion chamber and the amount of fueladmitted into the combustion chamber includes the step of adjusting thetiming of fuel admitted into the combustion chamber.
 12. A method ofcontrolling the burn rate in a diesel engine having a combustion chamberusing a target angle of the second peak of an ion current waveformcorresponding to a desired burn rate, the method comprising the stepsof: comparing a real time average of the crank shaft angle of the secondpeak of the ion current wave form to the target angle; and adjusting therate of fuel admitted into the combustion chamber such that the realtime average of the angle of the second peak of the ion current waveformis within a tolerance window of the target angle.
 13. The method ofclaim 12 wherein the step of adjusting the rate of fuel admitted intothe combustion chamber comprises the steps of: if the real time averageof the crank shaft angle of the second peak of the ion current wave formis advanced of the target angle, decreasing the rate of fuel admittedinto the combustion chamber until the real time average of the crankshaft angle of the second peak of the ion current wave form is within atolerance of the target angle; and if the real time average of the crankshaft angle of the second peak of the ion current wave form is retardedof the target angle, increasing the rate of fuel admitted into thecombustion chamber until the real time average of the crank shaft angleof the second peak of the ion current wave form is within a tolerance ofthe target angle.
 14. The method of claim 12 wherein the start ofinjection in a diesel engine is also controlled by the ion current waveform, the method further comprising the steps of: comparing the measuredcrank shaft angle of the rise of ion current to the target crank shaftangle corresponding to a desired start of combustion; and adjusting theinjection timing such that the crank shaft angle of the rise of ioncurrent is within a tolerance window of the target crank shaft angle.15. The method of claim 14 wherein the step of adjusting the injectiontiming comprises the steps of: retarding a start of injection angle tomove an early angle of the rise of ion current towards the target crankshaft angle for the next cycle; and advancing the start of injectionangle to move a late angle of the rise of ion current towards the giventarget crank shaft angle for the next cycle.
 16. A method forcontrolling the maximum power of a reciprocating engine having at leastone combustion chamber comprising the steps of: determining a target ioncurrent at a target angle corresponding to a desired burn rate;comparing an average ion current signal and crank shaft angle to thetarget ion current at the target angle; and adjusting an engine inputparameter into the at least one combustion chamber until the average ioncurrent signal and the crank shaft angle are within a tolerance windowof the target ion current at the target angle.
 17. The method of claim16 wherein the step of adjusting an input parameter includes adjustingone of a rate of fuel admitted into the combustion chamber and an amountof fuel admitted into the combustion chamber.
 18. The method of claim 16wherein the step of adjusting an input parameter includes adjusting thelevel of EGR admitted into the combustion chamber.
 19. A method forcontrolling the maximum power of a reciprocating engine having at leastone combustion chamber comprising the steps of: determining a target ioncurrent at a target angle corresponding to a desired burn rate;comparing an average ion current signal and crank shaft angle to thetarget ion current at the target angle; and adjusting at least one of anamount of EGR and a rate of EGR input into the at least one combustionchamber until the average ion current signal and the crank shaft angleare within a tolerance window of the target ion current signal at thetarget angle.
 20. The method of claim 19 wherein the step of adjustingcomprises the steps of: if the average ion current signal corresponds toa higher burn rate than the desired burn rate, increasing the at leastone of the amount of EGR and the rate of EGR admitted into thecombustion chamber; and if the average ion current signal corresponds toa lower burn rate than the desired burn rate, decreasing the at leastone of the amount of EGR and the rate of EGR admitted into thecombustion chamber.